Normalize the Python package name to "google-generativeai"

Description of the change

The package name google-generativeai was written as google.generativeai which is incorrect.

Use the correct package name on the pip install command.

Choose one: Bug fix

[x] I have performed a self-review of my code.
[x] I have added detailed comments to my code where applicable.
[x] I have verified that my change does not break existing code.
[x] My PR is based on the latest changes of the main branch (if unsure, please run git pull --rebase upstream main).
[x] I am familiar with the Google Style Guide for the language I have coded in.
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